Tendon and pressure actuation for a bio-inspired manipulator based on an antagonistic principle

This paper proposes a soft, inflatable manipulator that is antagonistically actuated by tendons and pneumatics. The combination of the two actuation mechanisms in this antagonistic robot structure is inspired by the octopus which uses its longitudinal and transversal muscles to steer, elongate, shrink and also stiffen its continuum arms. By 'activating' its antagonistic muscle groups at the same time, the octopus can achieve multiple motion patterns as well as stiffen their arms. Being organized in a similar fashion, our robot manipulator uses, on the one hand, pneumatic actuation and, on the other hand, tendon-based actuation - one opposing the other, achieving an overall antagonistic actuation framework. Controlling the pressure inside the robot while at the same time controlling the tendons' displacements, the robot can be moved into a wide range of configurations while simultaneously controlling the arm's stiffness. This paper builds on earlier work by the authors: Here, we present a new conic-shaped manipulator structure and the control architecture. Using a constant curvature model, we have derived an approach suitable for controlling the robot manipulator. The manipulator's reachable workspace is analyzed and proof-of-concept experiments were conducted to show the robot's stiffness control and motion abilities.